Post navigation

Prairie Response to Grazing and Drought

Fire, grazing, and drought are the three dominant forces that shape(d) our prairies over time. Because of the drought we experienced last year, many of our prairies experienced all three of those forces in the same season. We manage most of our sites with variations of patch-burn grazing. After we burn a portion (patch) of prairie, cattle concentrate their time within that burned patch, grazing it much more intensively than other portions of the same prairie until a new patch is burned. As a result, the dominant grasses are much weakened by the end of the season, temporarily opening space for opportunistic plants of many species.

Showy evening primrose is prominent among a number of profusely blooming plants in this restored prairie that was burned and intensively grazed during last year’s drought. The Nature Conservancy’s Platte River Prairies, Nebraska.

The patch of prairie in the above photo is not being grazed this year, which will allow the dominant grasses – still present, but much reduced in size and vigor – to recover. In the meantime, butterflies, bees, and other pollinators are enjoying an abundance of “weedy” flowers such as hoary vervain (Verbena stricta), showy evening primrose (Oenothera rhombipetala), yarrow (Achillea millefolium), upright prairie coneflower (Ratibida columnifera), black-eyed susan (Rudbeckia hirta), and many others. At the same time those pollinators can still find their regular fare of more “conservative” long-lived perennial forbs (prairie clovers and other legumes, perennial sunflowers and silphiums, etc.) – they are just visually obscured by the species responding positively to last year’s grazing and drought. If you’re interested, you can see some plant data from this site from a couple years ago that shows some trends in species frequency and floristic quality over time.

Here’s another photo of the same patch prairie, showing the diversity and abundance of opportunistic wildflower species and a thin, weakened (temporarily) stand of grass.

Another photo from the same prairie.

One of the aspects of fire/grazing management I enjoy most – and one that can make some people uncomfortable – is the variability in prairie response between years and between sites. Every time we burn/graze a prairie, we see somewhat different responses from the plant community, even if we’re using very similar timing and stocking rates each time. I think that’s great, and that it adds to the kind of messy, dynamic diversity I think is important in natural systems. That messiness helps prevent any species or group of species from becoming too dominant, but also helps ensure that each species has the opportunity to thrive and reproduce now and then.

Griffith Prairie (owned and managed by Prairie Plains Resource Institute of Aurora, Nebraska). The area shown in this photo was burned and grazed during the drought of 2012 in a way very similar to the Platte River Prairie shown earlier. However, the plant community response at Griffith was very different – including a big flush of deer vetch (Lotus unifoliolatus) and abundant reproduction of leadplant (Amorpha canescens), among other things. Visually, the prairie is very flowery this year because the vigor of the dominant grasses is suppressed from last year’s drought/grazing.

These days, I spend quite a bit of time thinking about the scale and arrangement of our management treatments across the landscape. For example, I’m not sure how big each of our within-prairie habitat patches should be. I don’t think it matters much to plants, but habitat patches have to be large enough for animals to live in, yet small enough that wildlife and insects don’t have to travel unreasonable distances to find appropriate habitat when conditions change from year to year. For example, voles living in a thatchy patch of unburned prairie will have to relocate when that patch gets burned. How far can they travel to find another patch of unburned prairie? What kinds of habitat do they need as they make that trip?

For now, we’re just doing what seems reasonable, but I’ll feel better if we can get some data to help us better evaluate the travel abilities of insects, snakes, small mammals, and others. Anybody looking for a career’s worth of research projects?

About Chris Helzer

Chris Helzer is the Director of Science for The Nature Conservancy in Nebraska. His main role is to evaluate and capture lessons from the Conservancy’s land management and restoration work and then share those lessons with other landowners – both private and public. In addition, Chris works to raise awareness about the importance of prairies and their conservation through his writing, photography, and presentations to various groups.
Chris is also the author of "The Ecology and Management of Prairies in the Central United States", published by the University of Iowa Press. He lives in Aurora, Nebraska with his wife Kim and their children.

Just wanted to add, that I love that your using various management techniques to manage prairies. Too often I see people with the mentality that the prairie has to be “left alone” and when that is done, the prairie often suffers. Thanks for the post. Thought I would also add that the four-point evening primrose is a plant that is found exclusively on sand prairies, from my experience.

Although it often seems conventional wisdom would have us believe there are inherent differences in the impact of bison and cattle on vegetation communities, they are in many ways more similar than different. Please explore the following references and note the common theme – the impact of either herbivore on vegetation communities likely has more to do with how either herbivore is managed than with inherent differences between the species. Thus, areas you might be familiar with where it seems as though cattle were destructive would likely look/be the same if they were being grazed by bison but managed the same way (management being stocking rate, season of use, etc.).

HI Chris, thank you for your hospitality last Friday, it was a fun day. What is the name of the Artemisia growing in the restored prairie near the sandhills. It was around 2-3’ tall, upright and forest green in color.
Bob H

Chris, In some of our highest quality prairies in the Eastern Tallgrass Region there are woodland/savannah plants under the “forest” of grass. Indeed, these plants seem to find the shade of certain grameoides (Carex stricta is a good one) to be just as acceptable as the shade provided by trees. I wonder if intense grazing would eliminate species that require cooling shade to survive a hot dry summer?

James, it’s possible that intense grazing year after year would eliminate plants as you say (though I think shading is not the major cause of those kinds of eradications). However, periodic grazing, followed by a couple years of recovery should allow most of those plants to stay in the system. Eastern prairies are certainly different than our more western sites, though, so I’m not advocating a NEED to graze them from a plant standpoint. I do, however, think it’s worth doing more experimentation with grazing in some cases, to see if habitat structure needs – especially for rare inverts and vertebrates – could be met through periodic grazing without doing damage to plant communities. In other words, it might not improve plant communities, but might improve habitat conditions without harming plant communities. Or maybe not – but I think it might be worth testing.

Chris, An example includes Arisaema triphyllum (Jack-in-the-pulpit) that grows under Carex strict a surprising distance away from the savannah edge in open treeless conditions. Another plant that ventures into prairies that provide enough shade or cooling ground water is Polemonium reptans (Jacobs Ladder). A last example of a shade loving plant that occurs in prairies is Trillium recurvatum (Prairie Trillium). I do not think any of these species could tolerate the baking sun they would need to endure to survive after an episode of heavy grazing and drought. None of these species are rare. Indeed, these species may not have originally occupied prairie habitats. A lack of grazing for a long period of time may have allowed them to spread into these habitats. I do not know.

James, I’m just getting to the comments posted, but you bring up an interesting question. How much shade is needed by these shade-loving species? My Ecology professor in college would use your example on a “field” quiz where he’d ask “What do these shade plants say about the history of the site that they are found?” Plants are good indicators of past management. When woodies are removed from a site there is a shift in the herbaceous plants. It sure makes managers think about the cause and effect of what they do.

One challenge with smaller prairies is how to integrate periodic grazing into a management regime. In some ways, it may be easier to burn a parcel than to get someone to graze it if the size of the prairie is relatively small. Do you know of individuals or organizations in Nebraska and Iowa that work with private landowners to do some episodic grazing? I suspect this would be giant hassle for the cattle owner, but I’d let them graze my place for free if I could get a couple nice steaks out of the deal.

Patrick, you might be surprised what you could get if you passed the word that you’re interested. Especially if someone is close by, we’ve had surprisingly good luck getting people to bring cows in even for a short period of time. Often, they are glad to be able to rest their own pasture for a month or so, and are willing to pay for the privilege. Much will depend upon travel distance, what you have for infrastructure, etc. You might be able to talk someone into building temporary fence and hauling water if you give them free grazing. Maybe you can get your steaks in the deal too – who knows?

Patrick I would echo Chris’ reply that you might be surprised at how willing livestock owners are to work with you on grazing a property. Additionally, you might also consider horses. I’ve used a neighbors horses for years to graze a remnant prairie and some reconstructions and I’ve really liked the results. For me they’re a vegetation management tool whereby all I do is specify the date they can be turned in and the date they need to be taken out. For the neighbor it’s free grass. Everyone involved has been pleased as punch.

However, I agree that in some instances grazing may not be the most feasible or desirable option, but I think that applies to any management option whether it is grazing, haying, burning, rest, etc. To highlight a consistent theme throughout Chris’ blog, the ideal situation would likely involve the periodic application of as many different management techniques/tools as possible to insure that conditions never remain static because stasis might lead to an undesirable level of dominance/prominence by the community members that do especially well in those conditions. Concurrently, those members of the community that don’t do well with a particular set of static conditions may become undesirably rare or lost from the community.

James – it’s a great question with a complicated answer (probably many answers). We generally haven’t worried too much about it, but try to be aware of where the cattle are coming from and what they’re being fed. It can sure be good to quarantine animals if there is a risk of truly invasive plants such as Sericea lespedeza coming in with (or through) animals. In our case, I don’t think there are many invasives that would come in that aren’t already present on our sites (fortunately or unfortunately).